The field of the present invention is that of lighting devices for a motor vehicle, such as a headlight with which the motor vehicle is equipped.
The vehicle lighting devices are conventionally used to project onto the road in front of the vehicle a lighting beam which enables the driver of the vehicle to drive in complete safety in night-time conditions.
These lighting devices are designed to light the road to a minimum regulatory distance for a high beam function and for a low beam function. This minimum distance, for example 300 meters for a high beam function, results in constraints in the light beam, notably in a portion of the beam situated between 3 and 15 meters in front of the vehicle.
In effect, to guarantee that a minimum lighting required at 300 meters is achieved, this lighting is often very great in the portion situated between 3 and 15 meters. Now, this is also regulated since the lighting in this area must not hamper the driver of the vehicle, notably by risking reducing the impression of long distance reach of the beam and/or risking dazzling the users other than the driver, by reflection on the surface of the wet road taken by the vehicle. The lighting in this portion situated between 3 and 15 meters in front of the vehicle is thus limited to 12 000 candelas at −4° measured along a horizontal axis in a vertical plane.
In the prior art devices, it is common practice to achieve this limit value of 12 000 candelas between 3 and 15 meters in order to succeed in providing the minimum lighting required at 300 meters.
In parallel with this situation, it is increasingly desirable to use the lighting beam of the vehicle to embed driving assistance information therein.
Now, when the portion of the beam situated between 3 and 15 meters is at the maximum tolerated lighting, it becomes impossible to embed an image by positive contrast. The only means available is then a negative contrast, but the latter is effective only if the information is delimited by an absence of light in the beam. In such a case, the area where the information is displayed is deprived of light and any road element in this area then becomes invisible to the driver. If for example, a pot hole deforms the road and the information covers this pot hole, the latter will be invisible to the driver who will not therefore be able to avoid it.
It is thus important to find another way of making the information visible in the beam while maintaining a level of safety for the driver of the vehicle.